Method for determining the required hardening conditions for cylindrical work pieces



Dec. 7, 1955 3. SEULEN ETAL 3,221,536

METHOD FOR DETERMINING THE QUIRED HARDENING CONDITIONS FOR CYLINDR L WORKPIECES Filed Sept. 14, 1962 2 Sheets-Sheet 1 Fig. 1

G. SEULEN ETAL 3,221,536

Dec. 7, 1965 METHOD FOR DETERMINING THE REQUIRED HARDENING CONDITIONS FOR CYLINDRICAL WORKPIECES 2 Sheets-Sheet 2 Filed Sept. 14, 1962 Jnven or United States Patent 3,221,536 METHOD FOR DETERMTNING THE REQUIRED HARDENING CONDKTIUNS FUR CYLINDRECAL WQRKPIECES Gerhard Seulen, Remscheid, and Herbert Geisel, Remscheid-Lnttringhausen, Germany, assignors to Deutsche Edelstahlwerlre Alrtiengesellschaft, Krefeld, and Allgerneine Elektricitilts, Berlin-Grunewald, Germany Filed Sept. 14, 1962, Ser. No. 223,724 Claims priority, application Germany, Sept. 18, 1961, D 37,054 6 (Claims. ((31. 7315.4)

The present invention relates to a method for determining the required hardening conditions for cylindrical workpieces. Cylindrical workpieces made of steel are often required to be hardened, particularly by methods which improve the strength of the workpiece at its surface. The surface hardening of cylindrical work is of importance in the production of steel cast and forged rolls for performing cold and hot rolling processes, as Well as of the back-up rolls associated with the work rolls. Such rolls are required to have an extremely hard surface whereas they must have a tough core to enable them to withstand the considerable mechanical stresses to which they are subjected when rolling down hot or cold sheet or strip. For the surface hardening of cold rolls methods have been developed which are based upon the generation of the hardening temperature at the surface by electroinductive means. It is a matter of vital importance that the hardening effect should penetrate into the work to a given depth. Hardened surface layers which are too thin cannot sustain the pressures which arise during rolling. Excessively thick hardened layers cause the mechanical properties of the core which have previously been adjusted to desirable values to be impaired by the hardening process.

Hitherto it was impossible to determine the hardening conditions necessary for achieving a given depth of penetration otherwise than by submitting a roll to a test. This sample roll had to be sectionalised in order to find out the depth of the hardened layer by visual inspection. This is a complicated as well as expensive procedure, espe cially if it proves to be necessary to make several such tests before the correct hardening conditions are found. Since the hardenability of rolls also depends upon the analysis of the material, the manner in which the melting process has been conducted, the forging procedure and heat treatment, different workpieces behave in different ways.

It is the object of the present invention to provide a method which can overcome these difliculties, and which will permit the conditions which lead to a given hardening result in a particular type of roll to be easily determined.

According to the invention the problem is solved by cutting segment-shaped prisms from disc-shaped sections cut from the cylinder. The flanks of these sample prisms are protected with a thermally insulating lagging and the prisms are then heated and quenched from the curved end face. The temperatures during this treatment can be continuously measured. Alternatively the treated sample can be examined merely by micrographic inspection of specimens taken from localised regions. If heating is performed electro-inductively, it is easy to determine the power density which has been used for the test.

The invention is based on the thought that in a cylindrical body which is evenly heated along the whole of its length, the heat can flow only radially inwards. The inventors recognized that it is quite suificicnt to reproduce the conditions obtaining in practice by using a sectorshaped sample prism with the resultant advantage of be ing in a position to test and examine, under widely differing conditions, a very large number of prisms taken from the body of only one roll in order to find the particular conditions which will produce a given depth of penetration of the hardened zone and a given hardness at the actual surface. These conditions can be easily applied to the practical case by applying the same power density for the same length of time. Although in this method a roll must be sacrificed for the purpose of testing, this may be a roll which for other reasons would have been rejected. More particularly, such a roll permits a whole series of tests under varying conditions to be performed, a possibility which does not arise in the conventional method.

According to a further feature of the invention allowance may be made for the subsequent removal of segmental samples When the rolls are cast or forged. The preferred procedure is to cut off the disc after the roll has been tempered but before it is subjected to the surface hardening treatment. This has the advantage that the nature of the material of the roll and of the samples is completely identical and that the workpiece as well as the samples have been submitted substantially to the same conditions of casting, forging and tempering.

In detail the procedure adopted may consist in finish forging the roll including the roll necks, one neck being forged to a greater length than is required. After having heat treated this roll, the surplus length can be cut off the longer neck by machining off a disc. In this procedure the disc will not have been as thoroughly worked as the roll, nor will it have the same diameter as the roll, but the sample disc can be very easily obtained so that the method will commend itself in many cases. From the optimum hardening conditions required for the sample conclusions can safely be drawn as to the hardening conditions which should be applied to the roll.

An alternative possibility is to forge a roll of somewhat excessive length and before forging the neck on to the end to machine a disc off the roll. If this procedure is adopted the sample disc can be thermally treated at the same time as the roll, so that the sample will be subjected to substantially the same treatment as the actual roll in every respect.

Yet another alternative consists in casting or forging a roll of excessive length with a neck at each end, one cast or forged neck being shorter than the neck at the other end. After having performed the termal treatment an annular disc is cut off the roll with an inner diameter corresponding with the outer diameter of the neck, whereas the outer diameter of the annulus will then be equal to that of the roll. Although the amount of machining this procedure involves is somewhat considerable a sample annulus is nevertheless obtained which with respect to its thermal treatment and the degree to which it has been Worked completely agrees with the remaining body of the roll. A similar result will be achieved if a roll with necks at each end is forged with a disc on the end of one of the necks, said disc corresponding in diameter with the diameter of the body of the roll. After the complete forging has been thermally treated the disc can be easily cut off. Although this latter procedure presents some difficulties with respect to forging technique, these can be readily overcome.

The method proposed by the present invention will now be illustratively described by reference to the drawings.

In the drawings,

FIGURE 1 is a plan View showing a roll in operative relation to an inductor for surface-heating it;

FIGURE 2 shows in end elevation a disc cut from such a roll and severed into sectors;

FIGURE 3 shows a sector produced from such a severed disc and;

FIGURE 4 shows a sector of modified cross-sectional contour formed from such a disc;

FIGURE 5 shows a suitable apparatus for subjecting a sector as aforesaid to heating and quenching incidental to hardening it and;

FIGURE 6 shows a shield device for shielding all save an arcuate end face of a sector during its heat treatment.

FIG. 1 schematically represents a roll 1. The surface of such a roll may be uniformly heated for instance by the rotary heating technique and then hardened by quenching, the roll being rotated in relation to a linear inductor 3 in the direction indicated by arrow 2 and the speed of rotation at the end of the process of heating being "so chosen that the entire cylindrical surface is evenly heated.

An alternative process consists in passing the roll 1 in the direction of arrow 4 axially through an inductor 5 and a following quenching spray 6.

For ascertaining the effect of given hardening conditions it was hitherto necessary to cut up the tempered surface-hardened roll into sections and to measure the depth of the hardened zone. If it was found that the conditions had not been suitably chosen and that considerably different hardening conditions would have been necessary to obtain the desired result, then a second roll had to be sacrificed without even then being certain of a satisfactory result.

The present invention therefore proposes to cut off from a roll, which may be a reject, a circular section 7 after the roll has been tempered and, has been described, such sections can be obtained by making provision for them when the roll is being actually forged. Such a circular section is then cut into sector shape prisms 8 as schematically indicated in FIG. 2. One such prism is shown in FIG. 3 on a larger scale. A heat insulating lagging 10 such as a packing of asbestos is applied to the side faces of the prism (one being marked 9). Thermocouples 12 may be inserted into holes drilled into the sides at varying distances from an end 11 of the prism.

If the sector-shaped prism is now heated through its end 11 by means of a suitable inductor, the resultant temperature distribution during the heating process and when cooling by quenching in the direction of the arrows 13 can be accurately observed. The conditions are exactly analogous to the conditions which would arise when heating and quenching by rotating the roll 1 in the direction of arrow 2 under a linear inductor 3 (FIG. 1).

On the other hand, if heating is performed by the axial feed method, that is to say if the roll is moved in the direction indicated by arrow 4 in relation to an inductor 5 and a quenching device 6, then a certain amount of heat will also flow in the axial direction of the cylinder. In order to reproduce the actual circumstances existing in practice when treating a roll in this way it is better to test segment-shaped prisms which, as shown in FIG. 4 have a height 14 substantially exceeding their width 15.

The most suitable width/ height ratio for each individual case can be readily determined by mathematical calculation.

After having been treated the prisms may be cut into slices and metallographically examined. If the selected conditions with respect to electric power, temperature achieved, hardening time and quenching rate fail to produce the desired hardening result, then the test can in practice be repeated any desired number of times by using further sample prisms, until eventually the desired set of conditions has been established. Even if it had been possible in the past to treat a roll already cut into sections a second time under different conditions, the desired result would nevertheless not have been achieved because annealing, followed by tempering and repeated surface hardening would not have provided comparable conditions.

The proposed method can be usefully employed also if surface hardening is performed with gas burners.

When performing the method by using inductors apparatus may be employed of the kind schematically illustrated in FIG 5. This comprises a carrier 15 for supporting the sector-shaped sample prism 8, the carrier being rotatably reciprocable about axis 16 in the direction of arrow 17 by drive means not specially shown. This reciprocatory motion may be optionally performed along two paths 18 and 19. The inductor 20 which in conventional manner consists of a hollow conductor with a laminar magnet yoke 21 is located adjacent path 18. The carrier first reciprocates underneath this inductor until the surface of the sample has reached hardeningtemperature. The carrier is then moved into the dotted position 8 and again reciprocated in path 19 opposite a quenching spray 22 until quenching has been completed. 12 are the holes intended for the reception of the thermocouples for measuring the temperature distribution during heating and quenching. Since in quenching it is desirable to prevent the quenching liquid from affecting the faces of the prism other than the end face 11 and from entering the holes 12, it may be advisable to provide a shield 23 shaped as indicated in FIG. 6. This shield may be placed over the sample prism 8 so as to expose only face 11 of the prism, whereas the side faces up to the edges at 24 are protected by the surface 25 of the shield. The best method to achieve the desired result is to weld the shield 25 to the prism 8 by a weld seam along the edges 24.

A particularly advantageous feature of the proposed method is that a prismatic sample can be supplied together with each cast or forged hot or cold roll delivered by the makers to a customer, so that the latter can check the depth of the hardened zone, the nature of the hardened structure and the hardness as such without having to sacrifice a roll for this purpose.

What we claim is:

1. A method for determining the hardening conditions required to bring about predetermined surface hardness and predetermined depth of penetration of the hardened zone of a work specimen having a cylindrical peripheral surface which specimen is to undergo a surface hardening treatment comprising: severing at least one sample from the work specimen, each sample including end faces and an arcuate face corresponding to said cylindrical peripheral surface of said specimen; applying thermal insulation to said end faces; heating and quenching at least one of said samples from said arcuate face thereof; examining the samples which have been heated and quenched for depth of penetration of the hardened zone and for the amount of surface hardness produced by the heating and quenching steps to determine which sample has achieved said predetermined surface hardness and said predetermined depth of penetration of the hardened zone thereof; heating and quenching said work specimen from the cylindrical peripheral surface thereof using essentially the same power density and quenching conditions as were used in the heating and quenching steps on the last-mentioned sample, thereby producing a surface hardness and depth of penetration of the hardened zone of said work specimen corresponding essentially to the surface hardness and depth of penetration of the hardened zone of said last-mentioned sample.

2. The method of claim 1 wherein the sample severed from the work specimen is a disk shaped section, said disc shaped section being further severed into segment shaped prisms prior to the heating and quenching thereof; and quenching each segment shaped prism using different power density and quenching conditions on each segment shaped prism from those used on each other of said segment shaped prisms.

3. The method according to claim 1, which is charac- 5 terised in that the temperature distribution is continuously measured during the heating and quenching of said sample.

4. The method according to claim 1, in which the Work specimen is cast or forged as a roll with end necks or journals and one neck or journal is formed of extra length and a disc-shaped section comprising the sample is cut off from that neck or journal.

5. The method according to claim 1, in which the work specimen is a roll and this is formed so that its length is excessive and a disc-shaped section comprising the sample is cut off the same before necks 0r journals are forged on to the roll.

6. The method according to claim 1, which comprises forging the work specimen as a roll of extra length including end necks or journals and so that one neck or journal is shorter than the other and then removing from the roll adjacent the shorter neck or journal an annular sample with an outside diameter equal to the outside diameter of the roll and an inside diameter equal to the outside diameter of the neck or journal.

References Cited by the Examiner FOREIGN PATENTS 927,122 4/1955 Germany. 435,343 9/1935 Great Britain.

LOUIS R. PRINCE, Primary Examiner.

DAVID SCHONBERG, RICHARD C. QUEISSER,

Examiners. 

1. A METHOD FOR DETERMINING THE HARDENING CONDITIONS REQUIRED TO BRING ABOUT PREDETERMINED SURFACE HARDNESS AND PREDETERMINED DEPTH OF PENETRATION OF THE HARDENED ZONE OF A WORK SPECIMEN HAVING A CYLINDRICAL PERIPHERAL SURFACE WHICH SPECIMEN IS TO UNDERGO A SURFACE HARDENING TREATMENT COMPRISING: SEVERING AT LEAST ONE SAMPLE FROM THE WORK SPECIMEN, EACH SAMPLE INCLUDING END FACES AND AN ARCUATE FACE CORRESPONDING TO SAID CYLINDRICAL PERIPHERAL SURFACE OF SAID SPECIMEN; APPLYING THERMAL INSULATION TO SAID END FACES; HEATING AND QUENCHING AT LEAST ONE OF SAID SAMPLES FROM SAID ARCUATE FACE THEREOF; EXAMINING THE SAMPLES WHICH HAVE BEEN HEATED AND QUENCHED FOR DEPTH OF PENETRATION OF THE HARDENED ZONE AND FOR THE AMOUNT OF SURFACE HARDNESS PRODUCED BY THE HEATING AND QUENCHING STEPS TO DETERMINE WHICH SAMPLE HAS ACHIEVED SAID PREDETERMINED SURFACE HARDNESS AND SAID PREDETERMINED DEPTH OF PENETRATION OF THE HARDENED ZONE THEREOF; HEATING AND QUENCHING SAID WORK SPECIMEN FROM THE CYLINDRICAL PERIPHERAL SURFACE THEREOF USING ESSENTIALLY THE SAME POWER DENSITY AND QUENCHING CONDITIONS AS WERE USED IN THE HEATING AND QUENCHING STEPS ON THE LAST-MENTIONED SAMPLE, THEREBY PRODUCING A SURFACE HARDNESS AND DEPTH OF PENETRATION OF THE HARDENED ZONE OF SAID WORK SPECIMEN CORRESPONDING ESSENTIALLY TO THE SURFACE HARDNESS AND DEPTH OF PENETRATION OF THE HARDENED ZONE OF SAID LAST-MENTIONED SAMPLE. 